For Lizards, Climate Change Is A Deadly — And Complex — Threat

Lizards are expected to be hard hit by climate change — and a new study suggests it might be even worse for some lizards than scientists thought.

Lizards are sensitive to global warming because they regulate their body temperature using the environment. They bask in the sun, and cool off in the shade. It's been predicted that about 40 percent of the world's lizard populations will die off by the year 2080, which means roughly 20 percent of lizard species will go extinct.

That prediction was based on certain assumptions about how easy it is for lizards to find shade, says Michael Sears, a biologist at Clemson University who was the study's lead author.

"The thing that those models assumed is that the lizard can find a piece of shade anywhere in the environment instantly if it needed it," says Sears. But in reality, of course, it takes lizards energy and time to find shade, which means those past predictions of extinction risk could be off-base.

He and his colleagues recently did a study using computer modeling and real-world experiments to see how the kind of shade available affects a lizard's ability to keep its body temperature in the optimal range.

The team surgically implanted tiny temperature sensors into dozens of spiny lizards, and then did experiments in special enclosures constructed in the New Mexico desert.

"We use these pieces of shade cloth to cool down temperatures in spots to see how the animals react to it," Sears says.

In the experiment, shade was arranged in different-sized clusters.

Michael Angilletta, Arizona State University, Michael Sears, Clemson University

What they found is that the lizards did much better when they had access to lots of small patches of shade, compared to just a few big patches, according to a report of their work in the Proceedings of the National Academy of Sciences.

"It's sort of like, if you were out jogging, and there was only one tree and it was a long way to the next one, and it was a hot day — that's a bad environment," says Sears. "But if there were a bunch of trees along the way providing little bits of shade, you'd feel a lot better."

That means predicting the future for lizards as the climate changes will be more complicated than people thought, as each population may be significantly affected by its local distribution of plants and rocky outcroppings that can provide shade.

In general, lizards that live in already-warm places will probably suffer from increased temperatures, while lizards that live in cool places might actually benefit to some extent, says Sears.

He adds that "everything in between, all bets are kind of off now. Because what our study suggests is that how bushes are placed in an environment might really impact the lizards just as much as the temperature itself."